1. Field of Invention
This invention relates specifically to a hydraulic rock drill designed for small mounted applications, incorporating characteristics that contribute to improved performance and easier maintenance.
2. Description of Prior Art
A percussive rock drill is a device that, in conjunction with a drill bit, uses rotation and percussive energy to drill a hole in rock for purposes of blasting, etc. Every fluid operated percussive rock drill includes certain basic features. A striking piston imparts impact energy to a drill steel and bit, and a valving mechanism directs the working fluid so as to cause reciprocating motion of the piston. A rotation mechanism causes the drill steel to rotate to give the bit a fresh rock surface to strike with each blow, and a drill steel retention mechanism allows retraction of the drill steel and bit when the hole is completed. Flushing fluid (typically air or water) travels through holes in the drill steel and bit to blow rock cuttings out of the drilled hole.
In a typical operation of a hydraulic rock drill, the striking piston is caused to reciprocate by variable hydraulic forces. The drill steel is constrained and located by a chuck mechanism and a steel retainer, and is caused to rotate by a mechanism such as a hydraulic motor driving through a gear reduction. A drill bit is attached to the end of the drill steel, and the combination of impact and rotation causes the drill bit to penetrate the rock. Finally, some type of fluid energy storage mechanism is used to provide relatively constant pressure sources of working fluid for the piston and rotation.
Manufacturers of small drilling rigs, designed to drill holes in the range of 1¼ to 2 inch diameter, typically use hand-held drills that are modified for mounted use. Modifications may be as simple as removing handles and locking control valves in the “on” position. The advantage of using hand-held tools in these applications is the simplicity of fluid connections; one supply and one exhaust hose serve both impact and rotation, as opposed to larger drills in which separate hoses are required for each function. One disadvantage of using hand-held tools is that rotation torque is typically low. Since the rotation robs power from the impact, rotation power is deliberately limited in order to maximize impact power. Another disadvantage is that if the rotation stalls, the impact power continues unabated or even increases, which can cause jamming of the drill bit into the drilled hole.